Phased array antennas are used in a variety of aerospace applications. A phased array antenna has a number of antenna elements that are aligned in phase to provide transmit or receive gain. By adjusting the amplitude and phase of the input signals from the different antenna elements using complex weights, interference sources can be isolated and rejected from the composite signal and the desired signal can be reinforced. One application for this isolation is use the phased array to eliminate interference sources for GPS (Global Positioning Satellite) receivers or to increase the received signal power through beam steering to the GPS satellites. There has been interest in using GPS for commercial aircraft navigation. However there are concerns about low power interference sources. A phased array antenna can be used to isolate these interference sources. The number of sources that can be isolated is related to the number of elements in the phased array. To obtain spatial diversity, the antenna elements need to be spaced so that the received signals are separated by one half cycle in phase. This means that the larger the number of elements the more space the phased array antenna requires. Since space in most aerospace application is at a premium, this has meant that the majority of installations only include a single antenna element which does not allow for spatial processing to isolate and reject interference sources.
Thus, there exists a need for a phased array antenna that is smaller than conventional phased array antennas while having the same number of elements and phase relationship between elements to provide spatial diversity for interference rejection.
In previous antenna designs, the size of the antenna element has been reduced through the use of a high dielectric substrate material. The size of the element is approximately equal to .lambda./2 by .lambda./2 inside the substrate material. However, this method does not reduce the over-all size of the antenna array as the antenna elements must be separated by the free-space .mu./2 to maintain the spatial diversity needed for interference rejection.
It would therefore be advantageous to provide a miniature phased array antenna system to reduce the over-all size of the array by using a high dielectric lens to maintain the signal spatial diversity between antenna elements while reducing the physical separation, and by using digital array phase-shifting electronics to reduce the size of the phased array antenna electronics.
In accordance with the illustrated preferred embodiment of the present invention, the miniature antenna employs a substrate having a high dielectric constant. A plurality of antenna elements are located on a surface of the substrate. A superstrate covers the antenna elements. The superstrate has a high dielectric constant, which reduces the physical size of a wave length of electromagnetic energy at the design frequency. The dielectric constant, thickness, and shape of the superstrate enable it to act as a dielectric lens for controlling the phased relationship of a signal received by the antenna elements. The design of the superstrate dielectric lens permits a reduction in the physical spacing between the antenna elements while maintaining spatial diversity in phase between signals arriving from different directions. This enables the antenna array to be made significantly smaller than conventional phased array antennas while maintaining a similar phase relationship to that achieved using conventional phased array antennas. Electronic circuitry coupled to each of the plurality of antenna elements applies complex weights to received signals prior to a summation thereof in order to reconstruct a desired signal and to deconstruct an undesired signal. Surface acoustic wave (SAW) filters employed in the electronic circuitry are temperature controlled to maintain group delay and phase stability.